JP7577129B2 - Liquid crystal polyester fiber and its manufacturing method - Google Patents

Description

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This application claims priority to Patent Application No. 2020-195469, filed in Japan on November 25, 2020, the entire contents of which are incorporated by reference into this application.

The present invention relates to liquid crystal polyester fibers and a method for producing the same.

Liquid crystal polyester fiber is a chemical fiber made of a polymer with a rigid molecular structure, and can be obtained by melt spinning liquid crystal polyester. Liquid crystal polyester fiber can exhibit extremely high mechanical properties by increasing the molecular weight of the polymer through solid-phase polymerization by heat treatment of the raw spun yarn obtained by melt spinning. Heat treatment in the solid-phase polymerization process requires high temperatures and a long time, but in order to improve productivity, many studies have been conducted on technologies to promote the polymerization reaction, such as increasing the molecular weight of liquid crystal polyester at low temperatures in a short time.

Regarding the polymerization of liquid crystal polyester, for example, Patent Document 1 (JP 2013-67779 A) describes a method for producing liquid crystal polyester in which a specific heteroaromatic compound is added as a catalyst to carry out melt polycondensation of a monomer mixture containing at least one monomer selected from the group consisting of terephthalic acid, terephthalic acid derivatives, 2,6-naphthalenedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid derivatives, and it is described that such a production method allows the reaction to proceed at a low temperature in a short time.

Furthermore, Patent Document 2 (WO 2017/68867) describes a method for producing a wholly aromatic polyester by polymerization using a fatty acid metal salt (specifically, potassium acetate) as a polymerization catalyst.

JP 2013-67779 A International Publication No. 2017/68867

Thus, Patent Documents 1 and 2 describe polymerization catalysts used during melt polymerization in the production of liquid crystal polyester, but none of them describe catalysts used in solid-phase polymerization after molding (e.g., melt spinning) the liquid crystal polyester obtained by melt polymerization.

Specifically, basic organic catalysts such as the heteroaromatic compounds described in Patent Document 1 are thermally decomposed during melt spinning of liquid crystal polyester at temperatures above 250°C, and therefore cannot be used in the subsequent solid-state polymerization.

In addition, the alkali metal ion catalyst described in Patent Document 2 has the effect of promoting side reactions such as depolymerization reactions as the molecular weight increases, which may have resulted in disadvantages such as a decrease in the attainable strength and a decrease in the heat aging resistance of the fiber after the solid-state polymerization process.

During the solid-state polymerization process, side reactions other than the polymerization reaction can occur that result in a decrease in strength, as well as phenomena such as the softening of the fiber surface causing the fibers to fuse together and lose flexibility. Therefore, a technology is needed that selectively allows only the polymerization reaction that contributes to improving mechanical properties to proceed at the lowest possible temperature and in the shortest possible time.

The present invention was made based on these problems, and aims to provide a liquid crystal polyester fiber that can exhibit excellent mechanical properties through low-temperature and short-time heat treatment and also has excellent heat aging resistance.

The inventors of the present invention conducted intensive research to achieve the above-mentioned object, and found that the polymerization catalysts that have been used in the past for melt polymerization cannot selectively promote the reaction in solid-phase polymerization, possibly because the reaction mechanism of solid-phase polymerization is different from that of melt polymerization. As a result of further research into catalysts suitable for solid-phase polymerization, they found that (i) by using a catalyst containing a specific metal element, it is possible to develop excellent mechanical properties at a low temperature and in a short time for heat treatment, and further, (ii) it is possible to suppress to a certain extent the progress of side reactions that cause a decrease in strength other than the polymerization reaction, and to improve the heat aging resistance of the heat-treated yarn obtained after the solid-phase polymerization process, and thus completed the present invention.

That is, the present invention can be configured in the following manner.
[Aspect 1]
A liquid crystal polyester fiber containing at least one metal element selected from the group consisting of metal elements of Groups 8 to 11 of the periodic table (preferably at least one metal element selected from the group consisting of copper, cobalt, and palladium).
[Aspect 2]
A liquid crystal polyester fiber according to aspect 1, wherein the content of the metal elements is 1 to 1000 ppm by weight (preferably 3 to 500 ppm by weight, more preferably 5 to 200 ppm by weight, and further preferably 10 to 100 ppm by weight).
[Aspect 3]
The liquid crystalline polyester fiber according to claim 1 or 2, wherein the metal element is contained as a metal compound, and the melting point of the metal compound is a melting point of the liquid crystalline polyester + 30°C or less (preferably a melting point of the liquid crystalline polyester + 20°C or less).
[Aspect 4]
A liquid crystal polyester fiber according to any one of aspects 1 to 3, having a strength of 18 cN/dtex or more (preferably 20 cN/dtex or more, more preferably 23 cN/dtex or more).
[Aspect 5]
A liquid crystal polyester fiber according to any one of aspects 1 to 4, wherein the total amount of one end is 20 meq/kg or less (preferably 3 to 15 meq/kg, more preferably 5 to 13 meq/kg).
[Aspect 6]
A liquid crystal polyester fiber according to any one of Aspects 1 to 5, wherein the liquid crystal polyester fiber has a ketone bond amount of 0.05 mol % or less (preferably 0.04 mol % or less, more preferably 0.02 mol % or less).
[Aspect 7]
A method for producing the liquid crystal polyester fiber according to any one of aspects 1 to 6, comprising melt-spinning a resin composition containing a liquid crystal polyester and at least one metal element selected from the group consisting of metal elements in Groups 8 to 11 of the periodic table (preferably at least one metal element selected from the group consisting of copper, cobalt, and palladium).
[Aspect 8]
A method for producing a liquid crystal polyester fiber according to aspect 7, wherein the content of the metal elements in the resin composition is 1 to 1000 ppm by weight in total (preferably 3 to 500 ppm by weight, more preferably 5 to 200 ppm by weight, and even more preferably 10 to 100 ppm by weight).
[Aspect 9]
The method for producing a liquid crystal polyester fiber according to aspect 7 or 8, wherein the metal element is contained in the resin composition as a compound having a melting point of the liquid crystal polyester + 30°C or less (preferably a melting point of the liquid crystal polyester + 20°C or less).
[Aspect 10]
The method for producing a liquid crystalline polyester fiber according to any one of aspects 7 to 9, further comprising heat-treating the raw spun yarn obtained by the melt spinning.
[Aspect 11]
A method for producing a liquid crystal polyester fiber according to claim 10, wherein the total carboxy terminal amount (total CEG amount) of the raw spinning yarn is 5.0 meq/kg or less (preferably 4.0 meq/kg or less, more preferably 3.0 meq/kg or less, even more preferably 2.5 meq/kg or less, and even more preferably 2.0 meq/kg or less).
[Aspect 12]
A fiber structure comprising at least a part of the liquid crystal polyester fiber according to any one of aspects 1 to 6.

In this specification, the term "liquid crystal polyester fiber" refers to a fiber composed of liquid crystal polyester, and is a concept that includes both raw spun yarn obtained by melt spinning and heat-treated yarn obtained by heat-treating the raw spun yarn.

It should be noted that any combination of at least two elements disclosed in the claims and/or the specification is included in the present invention. In particular, any combination of two or more of the claims described in the claims is included in the present invention.

The liquid crystal polyester fiber of the present invention can exhibit excellent mechanical properties by heat treatment at a low temperature for a short time. In addition, the liquid crystal polyester fiber after heat treatment has excellent heat aging resistance.

[Liquid crystal polyester fiber]
The liquid crystal polyester fiber of the present invention is composed of liquid crystal polyester. The liquid crystal polyester is composed of repeating units derived from, for example, aromatic diol, aromatic dicarboxylic acid, aromatic hydroxycarboxylic acid, etc., and the chemical structure of the aromatic diol, aromatic dicarboxylic acid, aromatic hydroxycarboxylic acid-derived units is not particularly limited as long as it does not impair the effects of the present invention. In addition, the liquid crystal polyester may contain a structural unit derived from an aromatic diamine, aromatic hydroxyamine, or aromatic aminocarboxylic acid, so long as it does not impair the effects of the present invention. For example, examples of preferred structural units are shown in Table 1.

In the structural units in Table 1, m is an integer from 0 to 2, and Y in the formula, in the range of 1 to the maximum number that can be substituted, each independently represents a hydrogen atom, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (e.g., an alkyl group having 1 to 4 carbon atoms, such as a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc.), an alkoxy group (e.g., a methoxy group, an ethoxy group, a isopropoxy group, a n-butoxy group, etc.), an aryl group (e.g., a phenyl group, a naphthyl group, etc.), an aralkyl group (e.g., a benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group), etc.), an aryloxy group (e.g., a phenoxy group), an aralkyloxy group (e.g., a benzyloxy group), etc.).

More preferred structural units include the structural units described in examples (1) to (18) in Tables 2, 3, and 4 below. When a structural unit in the formula is a structural unit that can exhibit multiple structures, two or more of such structural units may be combined and used as structural units that constitute the polymer.

In the structural units of Tables 2, 3 and 4, n is an integer of 1 or 2, and each structural unit n=1, n=2 may exist alone or in combination, and Y ₁ and Y ₂ may each independently be a hydrogen atom, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (e.g., an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc.), an alkoxy group (e.g., a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group, etc.), an aryl group (e.g., a phenyl group, a naphthyl group, etc.), an aralkyl group (e.g., a benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group), etc.), an aryloxy group (e.g., a phenoxy group, etc.), an aralkyloxy group (e.g., a benzyloxy group, etc.), etc. Of these, a hydrogen atom, a chlorine atom, a bromine atom, or a methyl group is preferred.

Z can also be a substituent represented by the following formula:

The liquid crystal polyester may preferably be a combination having a naphthalene skeleton as a structural unit. It is particularly preferable to include both a structural unit (A) derived from hydroxybenzoic acid and a structural unit (B) derived from hydroxynaphthoic acid. For example, the structural unit (A) may be represented by the following formula (A), and the structural unit (B) may be represented by the following formula (B). From the viewpoint of improving melt moldability, the ratio of the structural unit (A) to the structural unit (B) may be preferably in the range of 9/1 to 1/1, more preferably 7/1 to 1/1, and even more preferably 5/1 to 1/1.

The sum of the structural units (A) and (B) may be, for example, 65 mol% or more of the total structural units, more preferably 70 mol% or more, and even more preferably 80 mol% or more. In particular, liquid crystal polyesters in which the structural units (B) account for 4 to 45 mol% of the polymer are preferred.

The liquid crystal polyester may also contain a structural unit derived from 4-hydroxybenzoic acid as the aromatic hydroxycarboxylic acid, and may also contain a structural unit derived from an aromatic dicarboxylic acid and a structural unit derived from an aromatic diol. For example, at least one selected from the group consisting of the following formula (C) and the following formula (D) may be used as the structural unit derived from an aromatic dicarboxylic acid, and at least one selected from the group consisting of the following formula (E) and the following formula (F) may be used as the structural unit derived from an aromatic diol. Preferably, the liquid crystal polyester includes a structural unit (A) (above formula (A)) derived from 4-hydroxybenzoic acid, a structural unit (C) (below formula (C)) derived from terephthalic acid as an aromatic dicarboxylic acid, a structural unit (D) (below formula (D)) derived from isophthalic acid, and a structural unit (E) (below formula (E)) derived from 4,4'-dihydroxybiphenyl as an aromatic diol; a liquid crystal polyester including a structural unit (A) (above formula (A)) derived from 4-hydroxybenzoic acid, a structural unit (C) (below formula (C)) derived from terephthalic acid as an aromatic dicarboxylic acid, a structural unit (D) (below formula (D)) derived from isophthalic acid, a structural unit (E) (below formula (E)) derived from 4,4'-dihydroxybiphenyl as an aromatic diol, and a structural unit (F) (below formula (F)) derived from hydroquinone.

The liquid crystal polyester may contain structural units derived from 4-hydroxybenzoic acid, preferably 50 mol% or more, more preferably 53 mol% or more, and even more preferably 60 mol% or more. The upper limit of the content of structural units derived from 4-hydroxybenzoic acid in the liquid crystal polyester is not particularly limited, but may be, for example, 90 mol% or less, preferably 88 mol% or less, and more preferably 85 mol% or less.

The melting point (hereinafter, sometimes referred to as Mp ₀ ) of the liquid crystal polyester preferably used in the present invention is preferably in the range of 250 to 380°C, more preferably 255 to 370°C, even more preferably 260 to 360°C, and even more preferably 260 to 330°C. The melting point referred to here is the main absorption peak temperature observed when measured using a differential scanning calorimeter (DSC; Mettler "TA3000") in accordance with the JIS K 7121 test method. Specifically, 10 to 20 mg of a sample is taken and sealed in an aluminum pan in the DSC device, and then nitrogen is flowed as a carrier gas at 100 mL/min, and the endothermic peak is measured when the temperature is raised at 20°C/min. In cases where no clear peak appears in the first run in DSC measurement due to the type of polymer, the polymer should be heated at a rate of 50° C./min to a temperature 50° C. higher than the expected flow temperature, completely melted at that temperature for 3 minutes, cooled to 50° C. at a rate of 80° C./min, and then the endothermic peak should be measured at a heating rate of 20° C./min.

In addition, the liquid crystal polyester may contain thermoplastic polymers such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyamide, polyphenylene sulfide, polyether ether ketone, and fluororesin, as long as the effects of the present invention are not impaired. In addition, the liquid crystal polyester may contain various additives such as inorganic substances such as titanium oxide, kaolin, silica, and barium oxide, colorants such as carbon black, dyes, and pigments, antioxidants, ultraviolet absorbers, and light stabilizers.

The liquid crystal polyester fiber of the present invention contains at least one metal element selected from the group consisting of metal elements of Groups 8 to 11 of the periodic table. Preferably, it is at least one metal element selected from the group consisting of metal elements of Periods 4 to 6 and Groups 8 to 11 of the periodic table, and specifically, it may be at least one metal element selected from the group consisting of iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, and gold. Since the progress of the reaction in solid-phase polymerization can be promoted by the catalytic action of a specific metal element, the liquid crystal polyester fiber spinning raw yarn containing such a metal element as a solid-phase polymerization catalyst can exhibit excellent mechanical properties by low-temperature and short-time heat treatment. In addition, these metal elements can selectively promote the polymerization reaction and can suppress to some extent the progress of side reactions that cause strength reduction other than the polymerization reaction, so that the heat-treated yarn of the liquid crystal polyester fiber containing such a metal element has excellent heat aging resistance, that is, it can suppress the decrease in mechanical properties even if it is kept in a high-temperature environment for a long time.

From the viewpoint of promoting the polymerization reaction in solid-state polymerization, the metal element contained in the liquid crystal polyester fiber of the present invention may more preferably be at least one metal element selected from the group consisting of copper, cobalt, and palladium, and even more preferably be copper.

The above metal elements may be contained as metal compounds having a structure in which a metal atom is bonded to a nonmetallic atom. Examples of metal compounds include formates, acetates, propionates, butyrates, valerates, caproates, enanthates, caprylates, pelargonates, caprates, laurates, myristates, palmitates, stearates, naphthenates, benzoates, oxalates, malonates, succinates, adipates, terephthalates, isophthalates, phthalates, salicylates, tartrates, citrates, organic acid salts such as fluoroacetates, chloroacetates, bromoacetates, fluoropropionates, chloropropionates, and bromopropionates; inorganic acid salts such as sulfates, carbonates, and nitrates; halides such as fluorides, chlorides, bromides, and iodides; hydroxides; oxides; and sulfides. These metal compounds may be used alone or in combination of two or more. Among these metal compounds, for example, organic acid salts, inorganic acid salts, halides, and hydroxides are preferred from the viewpoint of having a low melting point and being able to improve dispersibility in the fibers.

The metal compound is not particularly limited as long as it acts as a solid-phase polymerization catalyst, but may be a metal compound that acts as a catalyst for decarboxylation of aromatic carboxylic acids, and may be a metal complex compound in which a metal atom is coordinated with a ligand from the viewpoint of promoting the polymerization reaction in solid-phase polymerization. The ligand is not particularly limited as long as it is a ligand that can be coordinated to a metal atom in the metal compound, but examples of the ligand include nitrogen-based ligands, oxygen-based ligands, carbon-based ligands, phosphorus-based ligands, and sulfur-based ligands. In the metal compound, an organic acid corresponding to the organic acid salt, an inorganic acid corresponding to the inorganic acid salt, or a halogen corresponding to the halide may be coordinated to the metal atom as a ligand.

The nitrogen-based ligand is not particularly limited as long as it is a ligand having a nitrogen atom capable of coordinating with the above metal atom, and examples thereof include amine-based ligands such as ammine (NH ₃ ), aniline, diisopropylamine, triethylamine, triphenylamine, hexamethyldisilazane, diazabicycloundecene, ethylenediamine (en), 2,3-butanediamine, N,N,N',N'-tetramethylethylenediamine, ethylenediaminetetraacetic acid (edta), diethylenetriamine, N,N,N',N'',N''-pentamethyldiethylenetriamine, 1,4,7-triazacyclononane, triethylenetetramine, tris(2-aminoethyl)amine, and hexamethylenetetramine; pyrrole, pyridine (py), and dimethylpyridine. Nitrogen-containing heteroaromatic ligands such as bipyridine (bpy), terpyridine, imidazole, pyrazole, pyrazine, pyrimidine, triazole, quinoline, isoquinoline, acridine, 1,8-naphthyridine, phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline, 4,7-diphenyl-1,10-phenanthroline, 2,9-diphenyl-1,10-phenanthroline, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, dimethylaminopyridine, and porphyrin; nitrile ligands such as acetonitrile and benzonitrile; cyanide (CN ⁻ ); isothiocyanide (NCS ⁻ ); and nitrosyl (NO).

The oxygen-based ligand is not particularly limited as long as it is a ligand having an oxygen atom capable of coordinating to the above-mentioned metal atom, and examples thereof include ether-based ligands such as dimethyl ether, diethyl ether, tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, etc.; alcohol-based ligands such as methanol, ethanol, phenol, 1,1'-binaphthalene-2,2'-diol, etc.; acyl-based ligands such as carboxylate (RCOO ^- ), oxalate (ox ^2- ), acetylacetonate (acac), etc.; aqua (H ₂ O); hydroxide (OH ^- ); oxo (O ^2- ); and the like.

The carbon-based ligand is not particularly limited as long as it has a carbon atom capable of being coordinated to the metal atom, but examples thereof include alkyl-based ligands such as methyl; aryl-based ligands such as phenyl; vinyl-based ligands; alkynyl-based ligands; carbene-based ligands such as N-heterocyclic carbene; alkene-based ligands such as ethylene and dibenzylideneacetone (dba); alkyne-based ligands such as acetylene and 2-phenylethynylbenzene; cyclopentadiene-based ligands such as cyclopentadiene and pentamethylcyclopentadiene; diene-based ligands such as 1,3-butadiene and 1,5-cyclooctadiene (cod); cyclic polyene-based ligands such as benzene and cyclooctatetraene; isocyanide-based ligands such as cyanomethylisocyanide and phenylisocyanide; carbonyl (CO), etc.

The phosphorus-based ligand is not particularly limited as long as it has a phosphorus atom capable of being coordinated to the metal atom. Examples of the phosphorus-based ligand include triphenylphosphine, tris(2-methylphenyl)phosphine, tris(2-methoxyphenyl)phosphine, di-tert-butylphenylphosphine, trimethylphosphine, tri-tert-butylphosphine, tricyclohexylphosphine, bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), 2,2'-bis(diphenylphosphino)propane (dppp), and bis(diphenylphosphino)methane (dppe). and phosphine-based ligands such as phosphine(diphenylphosphino)-1,1'-binaphthyl (BINAP), 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl (SPhos), 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl (XPhos), 2-dicyclohexylphosphino-2'-methylbiphenyl (MePhos), 2-dicyclohexylphosphino-2'-(N,N-dimethylamino)biphenyl (DavePhos), and 2-(di-tert-butylphosphino)biphenyl (JohnPhos).

The sulfur-based ligand is not particularly limited as long as it is a ligand having a sulfur atom capable of being coordinated to the metal atom, and examples thereof include thiol-based ligands; sulfoxide-based ligands such as dimethyl sulfoxide (DMSO); sulfur-containing heteroaromatic ligands such as thiophene, dibenzothiophene, and thiopyran; thiocyanide (SCN ⁻ ); and sulfide (S ²⁻ ).

The preferred ligand varies depending on the type of metal atom. In the case of copper, from the viewpoint of promoting the polymerization reaction in solid-phase polymerization, it is preferable that a nitrogen-based ligand is coordinated, more preferably that a nitrogen-containing heteroaromatic ligand or a nitrogen-based chelate ligand is coordinated, and even more preferably that a nitrogen-containing heteroaromatic chelate ligand is coordinated. Here, a chelate ligand is a ligand having two or more coordination sites in the molecule, and a ligand in which the multiple coordination sites are located at positions where one metal atom can be coordinated simultaneously. Examples of nitrogen-based chelate ligands include ethylenediamine, diethylenetriamine, triethylenetetramine, tris(2-aminoethyl)amine, hexamethylenetetramine, bipyridine, terpyridine, phenanthroline, and derivatives thereof.

The valence of copper in the copper compound may be zero, monovalent, or divalent, but from the viewpoint of avoiding aggregation and localization during melt spinning, it is preferable that it be monovalent or divalent, and from the viewpoint of promoting the polymerization reaction in solid-state polymerization, it is more preferable that it be monovalent.

In the case of cobalt, from the viewpoints of stability in the atmosphere during use and promotion of the polymerization reaction in solid-state polymerization, it is preferable that an oxygen-based ligand is coordinated, and it is more preferable that an acyl-based ligand is coordinated.

In the case of palladium, from the viewpoints of stability in the atmosphere during use and promotion of the polymerization reaction in solid-phase polymerization, it is preferable that an oxygen-based ligand is coordinated, and it is more preferable that an acyl-based ligand (e.g., carboxylate (preferably acetate, trifluoroacetate)) is coordinated.

The liquid crystal polyester fiber of the present invention can appropriately set the content of the metal element according to the type of the metal element, but for example, from the viewpoint of achieving a good balance between promoting the polymerization reaction in solid-phase polymerization and suppressing side reactions, the liquid crystal polyester fiber may contain the above metal elements in a total amount of 1 to 1000 ppm by weight, preferably 3 to 500 ppm by weight, more preferably 5 to 200 ppm by weight, and even more preferably 10 to 100 ppm by weight. The content of the metal element indicates the ratio of the total weight of the above metal element to the total weight of the liquid crystal polyester fiber, and when the metal element is contained as the above-mentioned metal compound, the content is indicated in terms of metal atoms. Here, the above content of the metal element may be the content of the metal element in the components constituting the fiber itself, excluding components attached to the fiber surface such as oils.

In the liquid crystal polyester fiber of the present invention, the content of alkali metals and alkaline earth metals may be less than 100 ppm by weight in total, preferably 10 ppm by weight or less, more preferably 5 ppm by weight or less, and even more preferably 1 ppm by weight or less, from the viewpoint of suppressing side reactions in solid-phase polymerization. Here, the above content of alkali metals and alkaline earth metals may be the content of alkali metals and alkaline earth metals in the components constituting the fiber itself, excluding components attached to the fiber surface such as oils. In this specification, alkali metals refer to lithium, sodium, potassium, rubidium, cesium, and francium, and alkaline earth metals refer to beryllium, magnesium, calcium, strontium, barium, and radium.

In addition, the liquid crystal polyester fiber of the present invention may contain 50% by weight or more of liquid crystal polyester, preferably 80% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, and even more preferably 99.9% by weight or more.

The liquid crystal polyester fiber spinning raw yarn of the present invention may have a total carboxy end amount (total CEG amount) of 5.0 meq/kg or less. Although the relationship between the carboxy group present at the molecular end of the liquid crystal polyester and the reaction in solid-phase polymerization is not clear, it is believed that reducing the amount of carboxy groups at the molecular end is one factor that activates the reaction in solid-phase polymerization, and it is believed that a spinning raw yarn with a small total carboxy end amount can exhibit excellent mechanical properties by low-temperature and short-time heat treatment. The total carboxy end amount (total CEG amount) of the liquid crystal polyester fiber spinning raw yarn may be preferably 4.0 meq/kg or less, more preferably 3.0 meq/kg or less, even more preferably 2.5 meq/kg or less, and even more preferably 2.0 meq/kg or less. The total carboxy end amount (total CEG amount) is a value measured by the method described in the examples below, and is the amount of carboxy groups present at the molecular ends in the molecules that mainly constitute the liquid crystal polyester fiber in 1 kg of fiber. For example, the carboxy group present at the polymer end in the liquid crystal polyester may be a carboxy group that remains unreacted in a structural unit present at such a polymer end, the structural unit being derived from a monomer having a carboxy group, such as an aromatic hydroxycarboxylic acid or an aromatic dicarboxylic acid.

The liquid crystal polyester fiber of the present invention may have a total one-terminal amount of 50 meq/kg or more, preferably 55 meq/kg or more, more preferably 60 meq/kg or more. It may also be 200 meq/kg or less, preferably 100 meq/kg or less. The total one-terminal amount indicates the number of polymer chains and is used as an index for evaluating the molecular weight. The larger the total one-terminal amount, the smaller the molecular weight, and the smaller the total one-terminal amount, the larger the molecular weight. Considering that it is difficult to quantify all types of terminals in liquid crystal polyester depending on the composition, in the present invention, the total one-terminal amount is defined as a value obtained by dividing the total amount (meq/kg) of carboxyl group terminals derived from hydroxycarboxylic acid and terminals from which carbon dioxide has been released by decarboxylation reaction in the carboxyl group derived from hydroxycarboxylic acid per 1 kg of liquid crystal polyester fiber by the molar ratio of the hydroxycarboxylic acid-derived structural unit in the liquid crystal polyester, and is a value measured by the method described in the examples described later. By heat-treating the raw spun yarn having a relatively large total amount of single terminals as described above, solid-state polymerization can be promoted and the total amount of single terminals can be reduced (i.e., the molecular weight can be increased).

The liquid crystal polyester fiber spinning yarn of the present invention can exhibit excellent mechanical properties by heat treatment at a low temperature and for a short time. In general, heat treatment of liquid crystal polyester fiber spinning yarn requires a long time (for example, about 20 hours) to improve the mechanical properties, and even when the heat treatment time is to be shortened, it is necessary to gradually increase the heat treatment temperature and perform heat treatment at a high temperature above the melting point of the spinning yarn, taking advantage of the fact that the melting point of the liquid crystal polyester fiber increases with the progress of solid-phase polymerization. In the present invention, when the strength of the liquid crystal polyester fiber spinning yarn is, for example, 12 cN/dtex or less, a heat-treated yarn with a strength of 18 cN/dtex or more can be obtained by heat treatment at a low temperature and for a short time. The low temperature and short time conditions vary depending on the heat treatment method and the amount of the raw spun yarn subjected to the heat treatment, but for example, in a batch-type heat treatment, the strength of the heat-treated yarn may be 18 cN/dtex or more, preferably 20 cN/dtex or more, and more preferably 23 cN/dtex or more, by heat-treating the liquid crystal polyester fiber at a temperature lower than the melting point (Mp) of the raw spun yarn for 3 hours or less. In the present invention, the liquid crystal polyester fiber may be regarded as a raw spun yarn when the strength is 12 cN/dtex or less, and may be regarded as a heat-treated yarn when the strength exceeds 12 cN/dtex.

The heat-treated yarn of the liquid crystal polyester fiber of the present invention may have a strength of 18 cN/dtex or more, preferably 20 cN/dtex or more, and more preferably 23 cN/dtex or more. The upper limit of the strength is not particularly limited, but may be, for example, about 40 cN/dtex. In the present invention, the strength of the liquid crystal polyester fiber refers to the tensile strength, and is a value measured by the method described in the examples below.

The heat-treated yarn of the liquid crystal polyester fiber of the present invention preferably has a high molecular weight from the viewpoint of improving mechanical properties such as strength, and for example, the total amount of terminal ends may be 20 meq/kg or less, preferably 15 meq/kg or less, and more preferably 13 meq/kg or less. The lower limit of the total amount of terminal ends is not particularly limited, but may be, for example, 3 meq/kg or more, and preferably 5 meq/kg or more.

From the viewpoint of improving mechanical properties such as strength, the heat-treated yarn of the liquid crystal polyester fiber of the present invention may have a ketone bond amount of 0.05 mol% or less, preferably 0.04 mol% or less, and more preferably 0.02 mol% or less. In the present invention, the ketone bond amount means the ratio of the molar amount of ketone bonds to the total molar amount of ester bonds and ketone bonds, and is a value measured by the method described in the examples below. If the ketone bond amount is too large, the strength of the liquid crystal polyester fiber tends to decrease, possibly due to a decrease in the linearity of the polymer. The lower limit of the ketone bond amount is not particularly limited, but may be, for example, 0.005 mol% or more.

The heat-treated yarn of the liquid crystal polyester fiber of the present invention may have a melting point of 290 to 400°C, preferably 300 to 380°C, and more preferably 305 to 350°C. The melting point of the liquid crystal polyester fiber is increased from the melting point (Mp) of the original spinning yarn by solid-phase polymerization. The melting point of the liquid crystal polyester fiber is a value measured by the method described in the examples below.

The heat-treated yarn of the liquid crystal polyester fiber of the present invention has excellent heat aging resistance, and the strength retention rate when heated at 250 ° C for 100 hours may be 70% or more, preferably 80% or more, more preferably 85% or more. In addition, the strength retention rate when heated at 250 ° C for 300 hours may be 50% or more, preferably 60% or more, more preferably 65% or more. Since it is preferable that the heat-treated yarn has a sufficiently high strength due to solid-phase polymerization, the strength retention rate when heated at 250 ° C for 100 hours or 300 hours may be 100% or less. The strength retention rate of the heat-treated yarn is a value measured by the method described in the examples described later.

The single fiber fineness of the liquid crystal polyester fiber of the present invention can be appropriately selected depending on the application, etc. For example, the single fiber fineness may be 0.5 to 50 dtex, preferably 1.0 to 35 dtex, more preferably 1.0 to 15 dtex, and even more preferably 1.5 to 10 dtex.

The liquid crystal polyester fiber of the present invention may be a monofilament or a multifilament. In the case of a multifilament, the number of filaments can be appropriately selected depending on the application, etc. For example, the number of filaments may be 5 to 5,000, preferably 10 to 4,000, and more preferably 30 to 3,000.

The total fineness of the liquid crystal polyester fiber of the present invention can be appropriately selected depending on the application, etc., and may be, for example, 10 to 50,000 dtex, preferably 15 to 30,000 dtex, and more preferably 25 to 10,000 dtex.

[Method of producing liquid crystal polyester fiber]
The method for producing a liquid crystal polyester fiber of the present invention may include at least a step of melt spinning a resin composition containing a liquid crystal polyester and at least one metal element selected from the group consisting of metal elements of Groups 8 to 11 of the periodic table.

The resin composition may contain the liquid crystal polyester described above and at least one metal element selected from the group consisting of metal elements in Groups 8 to 11 of the periodic table. The form in which the metal element is contained is not particularly limited, but it may be contained as the metal compound described above.

From the viewpoint of achieving a good balance between promoting the polymerization reaction in solid-state polymerization and suppressing side reactions, the resin composition may contain, for example, 1 to 1000 ppm by weight of the above metal elements in total, preferably 3 to 500 ppm by weight, more preferably 5 to 200 ppm by weight, and even more preferably 10 to 100 ppm by weight. The content of the metal elements in the resin composition indicates the ratio of the total weight of the added metal elements to the total weight of the resin composition including the liquid crystal polyester and the added metal elements, and when the metal elements are contained as the above-mentioned metal compounds, the content is indicated in terms of metal atoms.

From the viewpoint of promoting the polymerization reaction in solid-phase polymerization, the metal compound may be the metal complex compound described above. In this case, the metal compound may be mixed into the resin composition in such a manner that the metal complex compound already has a ligand coordinated thereto, or the metal compound and the compound that forms the ligand may be added separately to the resin.

The metal compound may be a compound having a melting point of the liquid crystal polyester (Mp ₀ ) + 30°C or less from the viewpoint of improving the long-term operability of melt spinning and improving dispersibility in the resin. In the melt spinning process, the resin composition is heated and melted at a temperature equal to or higher than the melting point (Mp ₀ ) of the liquid crystal polyester, but since the reaction related to solid-phase polymerization can be progressed to some extent even at this stage due to the catalytic action of the metal element in the resin composition, it is preferable to melt the metal compound together with the liquid crystal polyester in the resin composition to promote the reaction. The upper limit of the melting point of the metal compound is preferably Mp ₀ + 20°C or less.
From the viewpoint of processability, the melting point of the metal compound is preferably 400° C. or less, and more preferably 350° C. or less. The lower limit of the melting point of the metal compound is not particularly limited, but from the viewpoint of handleability in the vicinity of a melt spinning machine, it is preferably 100° C. or more.

Melt spinning can be carried out by known or conventional methods, for example, by melting the resin composition in an extruder, extruding it from a nozzle at a predetermined spinning temperature, and winding it up on a godet roller or the like.

The method for producing the liquid crystal polyester fiber of the present invention may further include a solid-phase polymerization step of heat-treating the raw spinning yarn obtained by melt spinning. The raw spinning yarn of the liquid crystal polyester fiber of the present invention can promote the reaction in the solid-phase polymerization due to the catalytic action of a specific metal element, so that the heat treatment in the solid-phase polymerization step can be performed at a low temperature for a short time.

From the viewpoint of promoting the polymerization reaction in the solid-phase polymerization, the raw spun yarn to be subjected to the solid-phase polymerization step may have a total carboxy terminal amount (total CEG amount) of 5.0 meq/kg or less, preferably 4.0 meq/kg or less, more preferably 3.0 meq/kg or less, even more preferably 2.5 meq/kg or less, and even more preferably 2.0 meq/kg or less. In the above melt spinning step, when the resin composition is heated and melted at a temperature equal to or higher than the melting point (Mp ₀ ) of the liquid crystal polyester, the amount of carboxy groups at the molecular terminals of the liquid crystal polyester can be reduced by desorbing carbon dioxide from the carboxy groups at the molecular terminals, possibly because the metal elements in the resin composition act as a catalyst for the decarboxylation reaction.

The method of heat treatment in the solid-state polymerization process is not particularly limited, and may be, for example, a batch-type heat treatment or a continuous heat treatment by conveying.

For example, in a batch-type heat treatment, the material may be wound around a bobbin in a packaged state, or in a skein or tow state, and it is preferable to perform the heat treatment in a packaged state, as this simplifies the equipment and improves productivity. The bobbin must be able to withstand the temperature of solid-state polymerization, and is preferably made of a metal such as aluminum, brass, iron, or stainless steel.

In the case of continuous heat treatment by conveying, the conveying method may be either contact conveying (for example, conveyor system, support roll system, heat treatment system using heated rollers) or non-contact conveying (roll-to-roll system). In addition, the processing path does not have to be a straight line, and turning rollers or guides may be placed in the device to appropriately change the length, angle, curvature, etc. of the processing path during heat treatment.

The solid-state polymerization process can be carried out by a known method, such as atmospheric heating or contact heating. The atmosphere is preferably air, an inert gas (e.g., nitrogen, argon), or a combination thereof. There is no problem if the solid-state polymerization is carried out under reduced pressure.

In the solid-phase polymerization process, the heat treatment temperature may be 230°C or higher, and from the viewpoint of efficient strength improvement, it may be preferably 240°C or higher, more preferably 250°C or higher. The heat treatment temperature may be lower than the melting point (Mp) of the raw spun yarn to be subjected to the solid-phase polymerization process to prevent melting. For example, in the range of 230°C or higher, it may be Mp-80°C or higher and lower than Mp°C, preferably Mp-50°C or higher and lower than Mp°C, more preferably Mp-30°C or higher and lower than Mp°C. In the present invention, excellent mechanical properties can be exhibited at a low heat treatment temperature, but since the melting point of the liquid crystal polyester fiber increases as the solid-phase polymerization progresses, it is sufficient to set the initial heat treatment temperature in the solid-phase polymerization process to be lower than the melting point (Mp) of the raw spun yarn, and from the viewpoint of efficient strength improvement, the heat treatment temperature may be increased stepwise according to the progress of the solid-phase polymerization, and heat treatment may be performed at a temperature higher than the melting point (melting point of the raw spun yarn) at the time of subjecting to the solid-phase polymerization process.

In the present invention, excellent mechanical properties can be exhibited by a short heat treatment, but the heat treatment time of the solid-phase polymerization process can be set appropriately depending on the heat treatment method and heat treatment temperature. As long as the desired mechanical properties can be exhibited, the heat treatment time is not particularly limited, but can be set, for example, in the range of 15 minutes to 15 hours, preferably 30 minutes to 10 hours, and more preferably 1 to 8 hours, and a short heat treatment time can be, for example, 15 minutes to 3 hours. The heat treatment time here refers to the retention time at a specified heat treatment temperature.

In the manufacturing method of the liquid crystal polyester fiber of the present invention, the strength ratio of the liquid crystal polyester fiber before and after the solid-phase polymerization process may be 1.5 times or more, preferably 1.8 times or more, and more preferably 2.0 times or more. The upper limit of the strength ratio of the liquid crystal polyester fiber before and after the solid-phase polymerization process is not particularly limited, but may be, for example, 10 times or less. Here, the strength ratio before and after the solid-phase polymerization process refers to the value obtained by dividing the tensile strength of the liquid crystal polyester fiber after the solid-phase polymerization process by the tensile strength of the liquid crystal polyester fiber (spinning raw yarn) before the solid-phase polymerization process.

In the method for producing liquid crystal polyester fibers of the present invention, for example, a known oil agent may be added before or after the solid-state polymerization step in order to improve the bundling of the fibers or to prevent fusion during heat treatment, and a compound containing an alkali metal or an alkaline earth metal may be added as described above.

The liquid crystal polyester fiber of the present invention can be suitably used for various fiber structures. Examples of the fiber structures include one-dimensional structures such as ropes and blended yarns, and highly processed products such as two-dimensional structures such as woven fabrics, knitted fabrics, and nonwoven fabrics. They can be used as various fiber products such as tension members (electric wires, optical fibers, heater wire core threads, cords for various electrical products such as earphone cords), sail cloths, ropes, sling belts, ropes, land nets, lifelines, fishing lines, fishing nets, and longlines. The fiber structures may be composed of liquid crystal polyester fibers alone, or may contain other components to the extent that the effects of the present invention are not impaired.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the following examples and comparative examples, various physical properties were measured by the following methods.

(Total fineness, single fiber fineness)
Based on JIS L 1013:2010 8.3.1 A method, the liquid crystal polyester fiber was wound into a skein of 1m per turn x 100 turns (total 100m) using a measuring device "Wrap Reel by Motor Drive" manufactured by Daiei Scientific Instruments Co., Ltd., and the weight (g) was multiplied by 100 to perform measurements twice per level, and the average value was taken as the total fineness (dtex) of the obtained liquid crystal polyester fiber. The quotient obtained by dividing this value by the number of filaments was taken as the single fiber fineness (dtex).

(Melting point of fiber and resin chips (granular molded body))
The melting point was determined as the main absorption peak temperature observed using a differential scanning calorimeter (DSC; Mettler, "TA3000") in accordance with JIS K 7121. Specifically, 10 to 20 mg of a sample was placed in an aluminum pan and sealed in the DSC apparatus, and nitrogen was passed as a carrier gas at a flow rate of 100 mL/min, and the endothermic peak derived from the liquid crystal polyester was measured when the temperature was raised from 25° C. at a rate of 20° C./min.

(Melting point of metal compound)
The measurement was performed using the same apparatus and pan as in the measurement of the melting point of the above fiber, except that in order to eliminate peaks of hydration water and residual solvent, nitrogen was flowed as a carrier gas at a flow rate of 100 mL/min, the temperature was raised from 25°C to 150°C at 20°C/min, held for 1 minute, cooled to 25°C at -20°C/min, and then the temperature was raised again from 25°C at 20°C/min, and the endothermic peak appearing at the lowest temperature was measured.

(Metal Element Content)
A liquid for analysis was prepared by the "microwave decomposition" described below, and the metal element content (ppm by weight) was determined by ICP-MS measurement.
Microwave decomposition Microwave decomposition was performed using a microwave decomposition device "ETHOS-1" manufactured by Milestone General Co., Ltd. 0.1 g of liquid crystal polyester fiber sample was weighed into a quartz insert, and 6 mL of nitric acid (1.42 mol/L) was added. The quartz insert was placed in a decomposition vessel containing 5 mL of water and 2 mL of hydrogen peroxide (concentration 30 to 36 wt%), and the vessel was sealed and subjected to microwave decomposition. After cooling, the volume was adjusted to 50 mL, and the filtrate was filtered through a 0.45 μm pore size filter and subjected to ICP-MS measurement.
ICP-MS Measurement The metal element content of the sample liquid prepared by the microwave decomposition was analyzed using an ICP-MS analyzer "Agilent 7900" manufactured by Agilent Technologies. The same sample liquid was measured three times in comparison with XSTC-622 (standard solution manufactured by SPEX) under conditions of a carrier gas flow rate of 0.7 L/min and an RF output of 1500 W, and the content of each metal element was determined from the average value.
In addition, when a sample has oil on it, such as a fiber, and there is concern about the influence of metal elements contained in the oil, it is recommended to remove the oil using the following method before performing microwave digestion.
Oil removal A liquid crystal polyester fiber sample in an amount of 100 g or less was placed in an aqueous solution in which 2 g of a nonionic surfactant (Actinol F-9, manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) was dissolved in 1 L of ion-exchanged water, and the temperature was adjusted to 60 to 90°C, followed by shaking for 40 minutes. The liquid crystal polyester fiber sample was removed and rinsed twice for 40 minutes with 1 L of ion-exchanged water adjusted to 60 to 90°C. The liquid crystal polyester fiber sample was removed and dried in an air atmosphere at 80°C for 3 hours or more using a hot air dryer "DN63HI" manufactured by Yamato Scientific Co., Ltd., to obtain a liquid crystal polyester fiber sample from which the oil was removed.

(Tensile strength)
With reference to JIS L 1013:2010 8.5.1, a tensile test was carried out six times for one yarn sample using an autograph "AGS-100B" manufactured by Shimadzu Corporation under conditions of a test length of 10 cm and a tensile speed of 10 cm/min, and the average tensile strength (cN) was divided by the total fineness (dtex) measured by the above-mentioned method to calculate the tensile strength (cN/dtex).

(Total CEG amount)
A liquid crystal polyester fiber sample was freeze-pulverized to d90=100 μm or less, and a large excess of n-propylamine was added to the pulverized sample, followed by heating and stirring at 40° C. for 90 minutes to decompose the sample. In this case, the ester bond present inside the polymer chain was decomposed into carboxylic acid n-propylamide and a hydroxy group, and the carboxy group (CEG) and hydroxy group present at the end of the polymer chain remained as carboxy group and hydroxy group, so that the decomposition products were separated by HPLC, and the amount of carboxy terminals (meq/kg) derived from each monomer was quantified by comparing the peak area of the decomposition products having a carboxy group with a calibration curve prepared by HPLC analysis of each sample. For example, the amount of CEG derived from a monovalent carboxylic acid such as 4-hydroxybenzoic acid or 6-hydroxy-2-naphthoic acid can be determined by quantifying 4-hydroxybenzoic acid or 6-hydroxy-2-naphthoic acid as is, and the amount of CEG derived from a divalent carboxylic acid such as terephthalic acid, isophthalic acid, or 2,6-naphthalenedicarboxylic acid can be determined by quantifying a substance in which one carboxy group is amidated, such as terephthalic acid mono-n-propylamide, isophthalic acid mono-n-propylamide, or 2,6-naphthalenedicarboxylic acid mono-n-propylamide. The sum of all the amounts of carboxy termini contained in each sample was taken as the total amount of carboxy termini (total CEG amount) (meq/kg) of that sample.

(Total end amount)
In the same manner as in the measurement of the total CEG amount, the liquid crystal polyester fiber sample was decomposed using n-propylamine, and the total amount (meq/kg) of the carboxy terminal amount derived from hydroxycarboxylic acid and the terminal amount resulting from the decarboxylation reaction of the carboxy group at the end derived from hydroxycarboxylic acid was quantified. For example, the terminal amount derived from 4-hydroxybenzoic acid was determined by quantifying 4-hydroxybenzoic acid and phenol, and the terminal amount derived from 6-hydroxy-2-naphthoic acid was determined by quantifying 6-hydroxy-2-naphthoic acid and 2-naphthol. In order to take into account the terminal amount derived from diols and dicarboxylic acids other than hydroxycarboxylic acid, the total terminal amount derived from hydroxycarboxylic acid was divided by the molar ratio of the structural unit derived from hydroxycarboxylic acid in the liquid crystal polyester of the sample, and the value was taken as the total one-terminal amount of the sample.

(Ketone binding amount)
The amount of ketone bonds was calculated by the pyrolysis gas chromatography method described in Polymer Degradation and Stability, 76, 85-94 (2002). Specifically, a liquid crystal polyester fiber sample was heated in the presence of tetramethylammonium hydroxide (TMAH) using a pyrolysis apparatus (manufactured by Frontier Labs, Inc., "PY2020iD") to generate gas by pyrolysis/methylation. This gas was analyzed using gas chromatography (manufactured by Agilent Technologies, Inc., "GC-6890N"), and the amount of ketone bonds (mol%) was calculated from the peak area derived from the ketone bonds and the peak area derived from the ester bonds.

(Heat aging resistance)
After twisting the yarn sample in the Z direction at 80 T/m, the liquid crystal polyester fiber was wound into a skein of 1 m per turn x 50 turns (total 50 m) using a measuring device "Wrap Reel by Motor Drive" manufactured by Daiei Scientific Seiki Seisakusho. The liquid crystal polyester fiber was heated at 250°C in an air atmosphere using a hot air dryer "DN63HI" manufactured by Yamato Scientific Co., Ltd. Two skeins were prepared per sample, one of which was heated for 100 hours and the other for 300 hours. During heating, the skein was hung on an arbitrary metal rod placed near the top of the furnace so that there was no contact other than the contact point with the metal rod. The average tensile strength (cN) of the sample after heating was measured using the above-mentioned method using the parts other than the contact point with the metal rod. This value was divided by the average tensile strength (cN) before heating in the heat aging resistance test, and the ratio was multiplied by 100 to obtain the strength retention (%) at 250° C. after 100 hours and 300 hours.

[Example 1]
The constituent units (A) and (B) shown in the formula below are (A) / (B) = 73 / 27 (mol ratio), and the content of alkali metals and alkaline earth metals is 10 weight ppm or less in total. Liquid crystal polyester resin (α) (Mp ₀ : 281 ° C.) chips (granular molded body) were added as a polymerization catalyst copper acetate (I) (manufactured by FUJIFILM Wako Chemical Co., Ltd., melting point 271 ° C.) powder so that the copper atom equivalent was 50 weight ppm (copper element content relative to the total amount of resin chips and polymerization catalyst), and mixed well with a shaker. The blend of resin chips and polymerization catalyst thus obtained was dried with hot air at 120 ° C. for 4 hours or more, and then melt extrusion was performed at a heater temperature of 300 ° C. with a Φ15 mm twin-screw extruder (manufactured by Technovel Co., Ltd., "KZW15TW-45MG-NH (-700)"), and the resin composition was supplied to the spinning head while being metered with a gear pump. At this time, a vacuum pump (Orion Machinery Co., Ltd. dry pump, "KRF40A-V-01B") was connected to a vent part in the middle of the twin-screw extruder via a metal tube, and the resin composition non-filled space in the twin-screw extruder was decompressed to 60 kPa. The temperature of the spinning head from the extruder outlet was set to 310 ° C. The spinning head was equipped with a spinneret with a hole diameter of 0.125 mmφ, a land length of 0.175 mm, and 50 holes, and the resin composition was discharged at a discharge rate of 28 g / min and wound on a bobbin at a winding speed of 1000 m / min to obtain a liquid crystal polyester fiber spinning raw yarn. At this time, a 2 wt% aqueous solution of sodium dodecyl phosphate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako First Grade) was applied to the spinning raw yarn from an oiling guide arranged directly under the spinning raw yarn. The amount of this aqueous solution applied was 1.4 g / min, and the adhesion ratio of sodium dodecyl phosphate to the spinning raw yarn was calculated to be 0.1 wt %.

Next, 4 kg of the spinning yarn thus obtained was rewound on an aluminum bobbin to a winding density of 0.6 g/ ^cm3 , and the temperature was raised from 25°C to 250°C in 2 hours in a nitrogen atmosphere using a closed oven, heat-treated at 250°C for 3 hours, and then cooled from 250°C to 25°C in 2 hours to obtain a heat-treated yarn of liquid crystal polyester filament. The analytical results of the obtained liquid crystal polyester fiber (spinning yarn and heat-treated yarn) are shown in Table 5.

[Example 2]
Two types of reagents, copper iodide (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) and an equimolar amount of 1,10-phenanthroline (Fujifilm Wako Chemical Co., Ltd.) were added to 5 L of acetonitrile (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) per 1 mol of copper iodide (I), and the suspension was stirred for 1 hour, filtered, and dried at 100°C for 3 hours to obtain an orange solid (melting point 300°C).
Except for using this solid as a polymerization catalyst in place of copper (I) acetate so as to give a copper atom equivalent of 50 ppm by weight, a liquid crystal polyester fiber raw spun yarn and a heat-treated yarn were obtained in the same manner as in Example 1. The analytical results of the obtained liquid crystal polyester fiber (raw spun yarn and heat-treated yarn) are shown in Table 5.

[Example 3]
A liquid crystal polyester fiber raw spun yarn and heat-treated yarn were obtained in the same manner as in Example 1, except that copper (II) acetate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako Grade 1, melting point 115° C.) was added as a polymerization catalyst instead of copper (I) acetate to a concentration of 50 ppm by weight in terms of copper atoms. The analysis results of the obtained liquid crystal polyester fiber (raw spun yarn and heat-treated yarn) are shown in Table 5.

[Example 4]
Two types of reagents, copper(II) sulfate pentahydrate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., special grade reagent) and 2 times the molar amount of 1,10-phenanthroline (manufactured by FUJIFILM Wako Chemical Co., Ltd.) relative to copper(II) sulfate pentahydrate, were added to 5 L of acetonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., special grade reagent) per mole of copper(II) sulfate pentahydrate, and the resulting suspension was stirred for 1 hour, filtered, and dried at 100°C for 3 hours to obtain a blue solid (melting point 294°C).
Except for using this solid as a polymerization catalyst in place of copper (I) acetate so as to give a copper atom equivalent of 50 ppm by weight, a liquid crystal polyester fiber raw spun yarn and a heat-treated yarn were obtained in the same manner as in Example 1. The analytical results of the obtained liquid crystal polyester fiber (raw spun yarn and heat-treated yarn) are shown in Table 5.

[Example 5]
A liquid crystal polyester fiber raw yarn and a heat-treated yarn were obtained in the same manner as in Example 1, except that cobalt (II) acetate tetrahydrate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., Wako special grade, melting point 194° C.) was added as a polymerization catalyst instead of copper (I) acetate to a concentration of 50 ppm by weight in terms of cobalt atoms. The analytical results of the obtained liquid crystal polyester fiber (raw yarn and heat-treated yarn) are shown in Table 5.

[Example 6]
A liquid crystal polyester fiber raw yarn and a heat-treated yarn were obtained in the same manner as in Example 1, except that palladium acetate (II) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako special grade, melting point 205° C.) was added as a polymerization catalyst instead of copper acetate (I) to a concentration of 50 ppm by weight in terms of palladium atoms. The analytical results of the obtained liquid crystal polyester fiber (raw yarn and heat-treated yarn) are shown in Table 5.

[Example 7]
A liquid crystal polyester fiber raw yarn and a heat-treated yarn were obtained in the same manner as in Example 1, except that the weight ratio of copper acetate (I) added to the resin was 5 ppm by weight in terms of copper atom. The analysis results of the obtained liquid crystal polyester fiber (raw yarn and heat-treated yarn) are shown in Table 5.

[Example 8]
A liquid crystal polyester fiber raw yarn and a heat-treated yarn were obtained in the same manner as in Example 1, except that the weight ratio of copper acetate (I) added to the resin was 500 ppm by weight in terms of copper atom. The analysis results of the obtained liquid crystal polyester fiber (raw yarn and heat-treated yarn) are shown in Table 5.

[Example 9]
To the chips (granular molded body) of the liquid crystal polyester resin (α) described in Example 1, copper acetate (I) powder (manufactured by Fujifilm Wako Chemical Co., Ltd., melting point 271 ° C.) was added as a polymerization catalyst to 500 ppm by weight in terms of copper atoms, and mixed well with a shaker. The blend of the resin chips and polymerization catalyst thus obtained was dried with hot air at 120 ° C. for 4 hours or more, and then melt extrusion was performed at a heater temperature of 300 ° C. with a Φ15 mm twin-screw extruder (manufactured by Technovel Co., Ltd., "KZW15TW-45MG-NH (-700)"), and the resin composition was supplied to the tip die while being metered with a gear pump. At this time, a vacuum pump (dry pump manufactured by Orion Machinery Co., Ltd., "KRF40A-V-01B") was connected via a metal tube from the vent part in the middle of the twin-screw extruder, and the resin composition non-filled space in the twin-screw extruder was depressurized to 60 kPa. The temperature from the extruder outlet to the tip die at this time was 310 ° C. At the tip die, the resin was discharged in a rod shape from a circular hole of φ3 mm at a discharge rate of 28 g / min, and while taking up this at a winding speed of 5 m / min, the rod-shaped resin composition was cut with a rotary cutter so that the major axis was 5 mm or less to obtain a resin composition chip. The resin composition chip thus obtained (mixed equivalent to 500 ppm by weight of copper element) and the liquid crystal polyester resin (α) chip were mixed in a weight ratio of 1:9, mixed well with a shaker, and dried with hot air at 120 ° C. for 4 hours or more. The blend of the two types of chips thus obtained was melt extruded at a heater temperature of 300 ° C. with a Φ15 mm twin-screw extruder (manufactured by Technovel Co., Ltd., "KZW15TW-45MG-NH (-700)"), and the resin composition was supplied to the spinning head while being metered with a gear pump. At this time, a vacuum pump (Orion Machinery Co., Ltd. dry pump, "KRF40A-V-01B") was connected to a vent part in the middle of the twin-screw extruder via a metal tube, and the resin composition non-filled space in the twin-screw extruder was decompressed to 60 kPa. The temperature of the spinning head from the extruder outlet was set to 310 ° C. The spinning head was equipped with a spinneret with a hole diameter of 0.125 mmφ, a land length of 0.175 mm, and 50 holes, and the resin composition was discharged at a discharge rate of 28 g / min and wound on a bobbin at a winding speed of 1000 m / min to obtain a liquid crystal polyester fiber spinning raw yarn. At this time, a 2 wt% aqueous solution of sodium dodecyl phosphate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako First Grade) was applied to the spinning raw yarn from an oiling guide arranged directly under the spinning raw yarn. The amount of this aqueous solution applied was 1.4 g / min, and the adhesion ratio of sodium dodecyl phosphate to the spinning raw yarn was calculated to be 0.1 wt %.
Next, 4 kg of the spinning yarn thus obtained was rewound on an aluminum bobbin to a winding density of 0.6 g/ ^cm3 , and the temperature was raised from 25°C to 250°C in 2 hours in a nitrogen atmosphere using a closed oven, heat-treated at 250°C for 3 hours, and then cooled from 250°C to 25°C in 2 hours to obtain a heat-treated yarn of liquid crystal polyester filament. The analytical results of the obtained liquid crystal polyester fiber (spinning yarn and heat-treated yarn) are shown in Table 5.

[Example 10]
A spinning stock yarn was obtained in the same manner as in Example 1, except that a spinneret with a hole diameter of 0.100 mmφ, a land length of 0.140 mm, and 100 holes was used. Then, a heat treatment was performed in the same manner as in Example 1 to obtain a heat-treated yarn. The analysis results of the obtained liquid crystal polyester fiber (spinning stock yarn and heat-treated yarn) are shown in Table 5.

[Example 11]
A spinning stock yarn was obtained in the same manner as in Example 1, except that a spinneret with a hole diameter of 0.150 mmφ, a land length of 0.210 mm, and 20 holes was used. Then, a heat treatment was performed in the same manner as in Example 1 to obtain a heat-treated yarn. The analysis results of the obtained liquid crystal polyester fiber (spinning stock yarn and heat-treated yarn) are shown in Table 5.

[Example 12]
A spinning raw yarn was obtained in the same manner as in Example 1, except that a spinneret with a hole diameter of 0.125 mmφ, a land length of 0.175 mm, and 20 holes was used, the resin composition was discharged at a discharge rate of 11.0 g/min, and the amount of sodium dodecyl phosphate aqueous solution applied from the oiling guide was 0.55 g/min. Then, heat treatment was performed in the same manner as in Example 1 to obtain a heat-treated yarn. The analysis results of the obtained liquid crystal polyester fiber (spinning raw yarn and heat-treated yarn) are shown in Table 5.

[Example 13]
Instead of the liquid crystal polyester resin (α) described in Example 1, a liquid crystal polyester resin (β) (Mp 0 : 348° C.) was used in which the molar ratio of each constituent unit shown in the following formula was (A)/(C)/(D)/(E)=65/10/5/20 and the content of alkali metals and alkaline earth metals was 10 ppm by weight or less in total, and the extruder heater temperature during melt extrusion was 360° C., and the temperature _of the spinning head from the extruder outlet was 360° C., except that a spun raw yarn was obtained in the same manner as in Example 1. Thereafter, a heat-treated yarn was obtained in the same manner as in Example 1, except that the heat treatment temperature of the spun raw yarn using a closed oven was 290° C. The analysis results of the obtained liquid crystal polyester fiber (spun raw yarn and heat-treated yarn) are shown in Table 5.

[Example 14]
Instead of the liquid crystal polyester resin (α) described in Example 1, a liquid crystal polyester resin (γ) (Mp 0 : 315° C.) was used in which the molar ratio of each structural unit shown in the following formula was (A)/(C)/(D)/(E)/(F)=54/15/8/16/7 and the content of alkali metals and alkaline earth metals was 10 ppm by weight or less in total, and the extruder heater temperature during melt extrusion was 340° C., and the temperature _of the spinning head from the extruder outlet was 350° C., except that a spun raw yarn was obtained in the same manner as in Example 1. Thereafter, a heat-treated yarn was obtained in the same manner as in Example 1, except that the heat treatment temperature of the spun raw yarn using a closed oven was 260° C. The analysis results of the obtained liquid crystal polyester fiber (spun raw yarn and heat-treated yarn) are shown in Table 5.

[Example 15]
A liquid crystal polyester fiber raw yarn and a heat-treated yarn were obtained in the same manner as in Example 2, except that the weight ratio of the orange solid (copper (I) iodide, 1,10-phenanthroline) added to the resin was 10 ppm by weight in terms of copper atom. The analysis results of the obtained liquid crystal polyester fiber (raw yarn and heat-treated yarn) are shown in Table 5.

[Example 16]
A liquid crystal polyester fiber raw yarn and a heat-treated yarn were obtained in the same manner as in Example 2, except that the weight ratio of the orange solid (copper (I) iodide, 1,10-phenanthroline) added to the resin was 20 ppm by weight in terms of copper atom. The analysis results of the obtained liquid crystal polyester fiber (raw yarn and heat-treated yarn) are shown in Table 5.

[Example 17]
A liquid crystal polyester fiber raw yarn and a heat-treated yarn were obtained in the same manner as in Example 2, except that the weight ratio of the orange solid (copper (I) iodide, 1,10-phenanthroline) added to the resin was 30 ppm by weight in terms of copper atom. The analysis results of the obtained liquid crystal polyester fiber (raw yarn and heat-treated yarn) are shown in Table 5.

[Example 18]
A liquid crystal polyester fiber raw yarn and a heat-treated yarn were obtained in the same manner as in Example 2, except that the weight ratio of the orange solid (copper (I) iodide, 1,10-phenanthroline) added to the resin was 70 ppm by weight in terms of copper atom. The analysis results of the obtained liquid crystal polyester fiber (raw yarn and heat-treated yarn) are shown in Table 5.

[Example 19]
A liquid crystal polyester fiber raw spun yarn and a heat-treated yarn were obtained in the same manner as in Example 2, except that the weight ratio of the orange solid (copper (I) iodide, 1,10-phenanthroline) added to the resin was 100 ppm by weight in terms of copper atom. The analysis results of the obtained liquid crystal polyester fiber (raw spun yarn and heat-treated yarn) are shown in Table 5.

[Example 20]
A liquid crystal polyester fiber raw yarn and a heat-treated yarn were obtained in the same manner as in Example 2, except that the weight ratio of the orange solid (copper (I) iodide, 1,10-phenanthroline) added to the resin was 150 ppm by weight in terms of copper atom. The analysis results of the obtained liquid crystal polyester fiber (raw yarn and heat-treated yarn) are shown in Table 5.

[Comparative Example 1]
Except for not mixing a polymerization catalyst and using only the chips of the liquid crystal polyester resin (α) as a raw material for spinning, the same procedure as in Example 1 was followed to obtain a liquid crystal polyester fiber raw spun yarn and a heat-treated yarn. The analysis results of the obtained liquid crystal polyester fiber (raw spun yarn and heat-treated yarn) are shown in Table 5.

[Comparative Example 2]
A liquid crystal polyester fiber raw yarn and a heat-treated yarn were obtained in the same manner as in Example 1, except that potassium acetate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., special grade reagent) was added as a polymerization catalyst instead of copper (I) acetate so as to be 50 ppm by weight in terms of potassium atom. The analysis results of the obtained liquid crystal polyester fiber (raw yarn and heat-treated yarn) are shown in Table 5.

[Comparative Example 3]
A liquid crystal polyester fiber raw yarn and a heat-treated yarn were obtained in the same manner as in Example 1, except that N,N-dimethyl-4-aminopyridine (DMAP) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako special grade) was added at a weight ratio of 1 wt % as a polymerization catalyst instead of copper acetate (I). The analysis results of the obtained liquid crystal polyester fiber (raw yarn and heat-treated yarn) are shown in Table 5.

[Comparative Example 4]
A liquid crystal polyester fiber raw yarn and a heat-treated yarn were obtained in the same manner as in Example 13, except that potassium acetate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., special grade reagent) was added as a polymerization catalyst instead of copper acetate (I) to a concentration of 50 ppm by weight in terms of potassium atom. The analysis results of the obtained liquid crystal polyester fiber (raw yarn and heat-treated yarn) are shown in Table 5.

[Comparative Example 5]
A liquid crystal polyester fiber raw yarn and a heat-treated yarn were obtained in the same manner as in Example 14, except that potassium acetate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., special grade reagent) was added as a polymerization catalyst instead of copper acetate (I) to a concentration of 50 ppm by weight in terms of potassium atom. The analysis results of the obtained liquid crystal polyester fiber (raw yarn and heat-treated yarn) are shown in Table 5.

As shown in Table 5, the raw spun yarns of Examples 1 to 20 contain specific metal elements, and the catalytic action of these elements makes it possible to obtain high-strength heat-treated yarns by heat treatment at low temperatures for a short period of time. Furthermore, the specific metal elements used in Examples 1 to 20 can selectively advance the reaction in solid-state polymerization and suppress the progression of side reactions that result in a decrease in strength, so the resulting heat-treated yarns have excellent heat aging resistance.

On the other hand, the raw spun yarn of Comparative Example 1 does not contain a catalyst, so solid-state polymerization does not proceed sufficiently with heat treatment at low temperature for a short time, and high-strength heat-treated yarn is not obtained. On the other hand, in the heat aging resistance test, solid-state polymerization proceeds due to heating in the test, and strength increases.

The raw spun yarn of Comparative Example 3 contains an organic catalyst used as a polymerization catalyst to synthesize liquid crystal polyester, but perhaps due to thermal decomposition during melt spinning, solid-state polymerization does not proceed sufficiently with heat treatment at low temperature and for a short time, as in Comparative Example 1 which does not contain a catalyst, and a high-strength heat-treated yarn is not obtained. On the other hand, in the heat aging resistance test, solid-state polymerization proceeds due to heating in the test, and strength increases.

Comparative Examples 2, 4 and 5 contain alkali metals, and high-strength heat-treated yarns can be obtained by heat treatment at low temperatures and for a short period of time. However, as a catalyst, they not only promote the reaction in solid-state polymerization but also promote side reactions. Therefore, in heat aging resistance tests, the strength of these yarns is significantly reduced compared to the heat-treated yarns of Examples 1 to 20, and they have inferior heat aging resistance.

The liquid crystal polyester fiber of the present invention can be used as various textile products such as ropes, nets, fishing nets, sling belts, tension members, etc.

As described above, a preferred embodiment of the present invention has been described, but various additions, modifications, or deletions are possible without departing from the spirit of the present invention, and such additions, modifications, or deletions are also included within the scope of the present invention.

Claims (14)

A liquid crystal polyester fiber containing at least one metal element selected from the group consisting of metal elements of Groups 8 to 11 of the periodic table, having a strength of 12 cN/dtex or less, and being subjected to a heat treatment . A liquid crystal polyester fiber containing at least one metal element selected from the group consisting of metal elements of Groups 8 to 11 of the periodic table and having a strength of 18 cN/dtex or more. 3. The liquid crystal polyester fiber according to claim 2 , wherein the total amount of terminal ends is 20 meq/kg or less. 4. The liquid crystal polyester fiber according to claim 2 , wherein the ketone bond amount is 0.05 mol % or less. The liquid crystal polyester fiber according to any one of claims 1 to 4 , wherein the total content of the metal elements is 1 to 1000 ppm by weight. The liquid crystal polyester fiber according to any one of claims 1 to 5 , wherein the metal element is contained as a metal compound, and the melting point of the metal compound is a melting point of the liquid crystal polyester + 30°C or less. 7. The liquid crystal polyester fiber according to claim 1, wherein the total content of alkali metals and alkaline earth metals is less than 100 ppm by weight. The liquid crystal polyester fiber according to any one of claims 1 to 7, wherein the liquid crystal polyester contained in the liquid crystal polyester fiber is composed of a combination of structural units represented by any one of the following formulas (1) to (16) and (18) .

In the formula, n is an integer of 1 or 2, and each of the structural units n=1 and n=2 may exist alone or in combination, Y1 _and Y2 _are each independently a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryl group, an aralkyl group, a phenethyl group, an aryloxy group, or an aralkyloxy group, and Z is any of the substituents represented by the following formula:

A method for producing the liquid crystal polyester fiber according to any one of claims 1 to 8 , comprising melt-spinning a resin composition containing a liquid crystal polyester and at least one metal element selected from the group consisting of metal elements in Groups 8 to 11 of the periodic table. A method for producing a liquid crystal polyester fiber according to any one of claims 2 to 4 and claims 5 to 8 when dependent on any one of claims 2 to 4, comprising melt-spinning a resin composition containing a liquid crystal polyester and at least one metal element selected from the group consisting of metal elements in Groups 8 to 11 of the Periodic Table, and heat-treating the raw spun yarn obtained by the melt spinning. The method for producing liquid crystal polyester fiber according to claim 10, wherein the total amount of carboxy terminals (total amount of CEG) of the raw spinning yarn is 5.0 meq/kg or less. The method for producing a liquid crystal polyester fiber according to any one of claims 9 to 11 , wherein the content of the metal elements in the resin composition is 1 to 1000 ppm by weight in total. The method for producing a liquid crystal polyester fiber according to any one of claims 9 to 12 , wherein the metal element is contained in the resin composition as a compound having a melting point of the liquid crystal polyester + 30 ° C or less. A fiber structure comprising at least a part of the liquid crystal polyester fiber according to any one of claims 1 to 8 .